The present invention relates to a method and system for transmitting data of moving picture, and apparatus for delivering and receiving data of moving picture, and particularly to a method of transmitting data of moving picture between information technology devices connected by an IP network as transmission lines, a transmission system using this transmission method, and data-delivering and data-receiving apparatus that constitute this transmission system.
When IP packets of data of moving picture are transmitted through the IP network of transmission lines, and particularly when the IP network is a wireless network, delay of the data of moving picture and dropout of packets may occur with ease depending upon the quality of the transmission lines. There is a prior art in which some error correction system is used to compensate for the lost packets, thus preventing the dropout of packets of moving picture data mentioned above. For example, in JP-A-09-116596, the property that the transmission lines cause sequential change of delay time is utilized such that the error correction system is switched on and off after measuring the transmission delay time.
In addition, when digital broadcasts are received, although decoding the data of a digital broadcast will cause delay in the reproduced output, the next channel broadcast is required to fast display when the user changes channels. To meet this requirement, the prior arts of, for example, JP-A-2001-094892 and JP-A-2000-115003 are proposed. In these documents, the data on the adjacent channels are previously decoded into images, and when channels are selected or switched, the images on the selected channels can be quickly displayed.
Moreover, the prior arts regarding the error correction system are proposed. That is, to detect error, the data link layer of the data transmission side monitors the dropout status of data and controls the amount of error correction code (in JP-A-2002-359609) or the way that redundant code systems and retransmission systems are combined is devised (in General meeting of Institute of Electronics, Information and Communication Engineers, B-6-195, 2003), thus improving the data transmission quality and reducing the transmission delay.
The prior art described in JP-A-09-116596 considers the delay of data on transmission lines, but does not take into account the delay in the error correction system itself. In addition, the prior arts described in JP-A-2001-094892 and JP-A-2000-115003 consider the delay caused when the video sources are switched, but do not allow for the same delay in the error correction system as in JP-A-09-116596. The prior art described in JP-A-2002-359609 does not consider the delay caused when the video sources are switched. The prior art described in document B-6-195 of Institute of Electronics, Information and Communication Engineers, 2003 does not take into account the answer to the fast-displaying request from a particular receiver although the moving-image packets that cannot be rectified by error correction can be compensated for by a combination with a retransmission system.
In other words, the above-given prior arts all have the problem that, when user switches the video sources (such as frequent switching of channels and starting to reproduce the recorded programs) in the moving-picture transmission system, the new video source cannot be started to fast display.